The histology and differential diagnosis of Spitz nevus.

We attempted to identify features by which Spitz nevi (SN) and melanomas that resemble SN may be distinguished, by examining the light microscopic features of 43 SN, using a multifactorial protocol. The data confirm that SN evolve in a manner similar to melanocytic nevi, with well-defined junctional, compound, and intradermal phases. Because of their growth kinetics most SN are excised at the compound stage, the most readily identifiable stage of evolution. However, almost 20% of SN are removed before or after the compound stage and at these stages they are recognized less readily. There are common characteristics of the histological features of the epidermis, junctional and dermal melanocytes, and stromal components at the different stages of SN evolution, but each stage additionally has unique characteristics. Each stage of SN has to be separated from different benign and malignant melanocytic lesions and criteria by which these separations may be made are discussed.